1. Field of the Invention
The present invention relates to a method of fabricating a semiconductor device, and more particularly, it relates to a method of fabricating a semiconductor device such as a thin-film transistor.
2. Description of the Prior Art
In relation to a liquid crystal display recently rapidly coming into wide use, it is required to prepare a thin-film transistor (hereinafter referred to as a polycrystalline silicon TFT) employing a polycrystalline silicon film formed on a substrate as an active layer at a low cost, in order to provide a lightweight and compact display of high performance at a low cost. In general, the maximum temperature in a fabrication process for a polycrystalline silicon TFT is reduced from about 1000xc2x0 C. to not more than about 600xc2x0 C., thereby enabling employment of a low-priced glass substrate in place of a high-priced quartz substrate. The fabrication process for a polycrystalline silicon TFT employing the low-priced glass substrate is generally referred to as a low-temperature process.
In relation to the conventional low-temperature process, known is excimer laser annealing (ELA) for crystallizing an amorphous silicon film employed as a starting material thereby forming a polycrystalline silicon film. In this ELA, the amorphous silicon film is irradiated with a short-wave laser beam of about 200 nm having high absorptivity for the amorphous silicon film or a polycrystalline silicon film by pulse oscillation of several 100 ns, thereby heating the amorphous silicon film or the polycrystalline silicon film to a high temperature and performing crystallization.
In the conventional ELA, however, beam intensity is dispersed due to instability of the pulse oscillation, and hence it is difficult to uniformly perform heating. Therefore, the yield is reduced to disadvantageously reduce productivity.
An object of the present invention is to provide a method of fabricating a semiconductor device capable of improving productivity by efficiently polycrystallizing an amorphous silicon film.
Another object of the present invention is to improve the yield in crystallization of the amorphous silicon film in the aforementioned method of fabricating a semiconductor device.
A method of fabricating a semiconductor device according to an aspect of the present invention comprises steps of forming an amorphous film on a substrate, forming a conductor film on the substrate, arranging the substrate so that the surface of the conductor film is substantially parallel to an electric field in a waveguide, and irradiating the conductor film with an electromagnetic wave thereby making the conductor film generate heat and crystallizing the amorphous film with the heat.
In the method of fabricating a semiconductor device according to this aspect, the substrate is so arranged that the surface of the conductor film is substantially parallel to the electric field in the waveguide as hereinabove described thereby improving absorptivity of the conductor film with respect to the electromagnetic wave, whereby the conductor film can be efficiently heated. Thus, crystallization can be performed in a short time, thereby improving productivity. When a conductor film having stable absorptivity is employed, the amorphous film can be uniformly heated regardless of the surface state thereof due to indirect heating through the conductor film having stable absorptivity, whereby the yield can be improved in crystallization of the amorphous film. The productivity can be improved also according to this.
In the aforementioned method of fabricating a semiconductor device according to this aspect, the step of arranging the substrate preferably includes a step of arranging the substrate on a position separated from a reflecting end surface for the electromagnetic wave at an interval of substantially odd times xcex/4 assuming that xcex represents the wavelength of the electromagnetic wave. According to this structure, the absorptivity of the conductor film for the electromagnetic wave is further improved, whereby the conductor film can be more efficiently heated.
In the aforementioned method of fabricating a semiconductor device including the step of arranging the substrate on the position separated from the reflecting end surface for the electromagnetic wave at the interval of substantially odd times xcex/4, the reflecting end surface for the electromagnetic wave may include a reflector provided to block an end of the waveguide. The step of arranging the substrate preferably includes a step of arranging the substrate while interposing a spacer member, transparent with respect to the electromagnetic wave, having a thickness of substantially odd times xcex/4. According to this structure, the substrate can be readily arranged on the position separated from the reflecting end surface for the electromagnetic wave at the interval of substantially odd times xcex/4.
In the aforementioned method of fabricating a semiconductor device including the step of arranging the substrate on the position separated from the reflecting end surface for the electromagnetic wave at the interval of substantially odd times xcex/4, the step of crystallizing the amorphous film preferably includes steps of arranging an electromagnetic convergent lens on the forward end of the waveguide and irradiating the surface of the conductor film with the electromagnetic wave converged by the electromagnetic convergent lens. According to this structure, the conductor film can be concentrically irradiated with a linear or point electromagnetic wave. In this case, the step of crystallizing the amorphous film may include steps of setting a reflector reflecting the electromagnetic wave and irradiating the reflector with the electromagnetic wave converged by the electromagnetic convergent lens and moving the substrate in parallel with the reflector while maintaining a distance of substantially odd times xcex/4 from the reflector for the electromagnetic wave. According to this structure, crystallization can be continuously performed over the entire conductor film, whereby crystallization can be readily performed also on a large-sized substrate.
In the aforementioned method of fabricating a semiconductor device including the step of arranging the substrate on the position separated from the reflecting end surface for the electromagnetic wave at the interval of substantially odd times xcex/4, the step of crystallizing the amorphous film preferably includes a step of providing a slit in the waveguide and linearly emitting the electromagnetic wave from the slit of the waveguide thereby irradiating the surface of the conductor film with the electromagnetic wave. According to this structure, the conductor film can be readily concentrically irradiated with a linear electromagnetic wave. In this case, the step of crystallizing the amorphous film includes steps of setting a reflector reflecting the electromagnetic wave and irradiating the reflector with the electromagnetic wave linearly emitted from the slit of the waveguide and moving the substrate in parallel with the reflector while maintaining a distance of substantially odd times xcex/4 from the reflector for the electromagnetic wave. According to this structure, crystallization can be continuously performed over the entire conductor film, whereby crystallization can be readily performed also on a large-sized substrate.
In the aforementioned method of fabricating a semiconductor device including the step of arranging the substrate on the position separated from the reflecting end surface for the electromagnetic wave at the interval of substantially odd times xcex/4, the step of crystallizing the amorphous film preferably includes a step of providing an opening for passing the substrate therethrough on the waveguide, providing a choke structure in the vicinity of the opening and inserting the substrate from the opening and passing the substrate through the waveguide while maintaining a distance of substantially odd times xcex/4 from the reflecting end surface for the electromagnetic wave. In this case, the structure provided with the opening for passing the substrate therethrough can be rendered equivalent to that provided with no opening in view of a high-frequency circuit due to the choke structure. Thus, no leakage of a microwave or the like may be taken into consideration also when the opening is provided. When the substrate is inserted from the opening and passed through the waveguide, crystallization can be continuously performed over the entire conductor film, whereby crystallization can be readily performed also on a large-sized substrate.
In the aforementioned method of fabricating a semiconductor device according to this aspect, the step of crystallizing the amorphous film preferably includes steps of forming the waveguide by folding a linear waveguide a plurality of times while providing a plurality of openings for passing the substrate therethrough on high-field portions of the side surface of the waveguide and moving the substrate to pass through the plurality of openings. According to this structure, the conductor film of the substrate can be continuously irradiated with the electromagnetic wave, whereby the conductor film can be efficiently heated. Thus, crystallization can be performed in a short time, thereby improving productivity.
In the aforementioned method of fabricating a semiconductor device according to this aspect, the step of crystallizing the amorphous film preferably includes a step of irradiating the conductor film with a pulsing electromagnetic wave thereby making the conductor film generate heat and crystallizing the amorphous film with the heat. When the conductor film is thus irradiated with the pulsing electromagnetic wave, crystallization can be performed by short-time heating.
In the aforementioned method of fabricating a semiconductor device according to this aspect, the step of crystallizing the amorphous film preferably includes a step of irradiating the conductor film with the electromagnetic wave while moving at least either the substrate formed with the conductor film or the electromagnetic wave thereby making the conductor film generate heat and crystallizing the amorphous film with the heat. According to this structure, crystallization can be readily continuously performed over the entire conductor film.
In the aforementioned method of fabricating a semiconductor device according to this aspect, the electromagnetic wave preferably includes a microwave, and the conductor film preferably includes a resistor film. In this case, the resistor film can be readily heated with the microwave.
In the aforementioned method of fabricating a semiconductor device according to this aspect, the conductor film may include a polysilicon film. Further, the amorphous film may include an amorphous silicon film.
The foregoing and other objects, features, aspects and advantages of the present invention will become more apparent from the following detailed description of the present invention when taken in conjunction with the accompanying drawings.